Brumas, once the rim is suitably smoothed, carefully pour a half a bottle of beer [Adnam's] into the tumbler then run the pad of your [already] wetted finger-tip slowly around the rim ... you should hear a perfect harmonic musical note ring out ... then commence to a-drinkin' the amber nectar, :o]

No, still think that Mechkb 2 answer is the way to go, be a man and get that sander growling.

Please remember to wear safety glasses and hard hat at all times, gloves are not recommended as they could be a snagging hazard on the belt sander. Nearly forgot, safety boots are a must have in case you drop the sander.